The present invention relates to a step variable transmission for a motor vehicle, wherein the step variable transmission has a plurality of forward gear stages and at least one reverse gear stage.
The present invention more precisely relates to an automatic step variable transmission in which the engagement and disengagement of gear stages is carried out by means of actuators. Selector drums, which are driven electromotively, hydraulic linear actuators, etc. can be used as actuators.
The present invention relates in particular to twin-clutch transmissions and automatic shift transmissions.
Twin-clutch transmissions are for example known from the documents DE 198 21 164 A1, EP0 083 747 A2, EP0 046 373 A1.
Automatic shift transmissions are provided in the Smart®, in the BMW® M3 and in the recently introduced BMW® M5. The latter involves a 7-gear automatic shift transmission. Said automatic shift transmission has a wheel set arrangement which does not follow the conventional H-pattern. In particular, shift clutch packs which have two shift clutches are assigned to not directly successive gears. Since the shift clutch packs have separate actuators in each case, the disengagement of a source gear and the engagement of a target gear can take place with a certain time overlap, so that gear changes can be carried out very quickly.
In twin-clutch transmissions, the forward gears are divided between two partial transmissions. Here, it is generally the case that odd gears are assigned to one partial transmission and even gears are assigned to the other partial transmission. Each partial transmission is connected by means of a separate clutch to the drive output shaft of the drive motor. With a twin-clutch transmission, gear changes can be carried out without an interruption in tractive force by means of overlapping actuation of the two clutches.
The two transmissions types (twin-clutch transmission and automatic shift transmission) however still do have room for improvement.